CBRS for the Wireless LAN Engineer

by | Oct 17, 2019 | Blog

There has been a lot of talk lately about this CBRS or Private LTE technology.

Actually, it has been talked about for years and years. But it is finally nearing a stage to come to market and be installed in an enterprise near you.

First, CBRS does NOT use 802.11 protocols. It works off of the same type of technologies and protocols as your cellular LTE on your smartphone. It uses a set of frequencies from 3.55 GHz to 3.7 GHz. About 150 MHz of bandwidth. This is about double what we have in 2.4GHz in the US, and about a third of what we have now in the 5GHz range.

The second big difference between CBRS and Wi-Fi is the FCC’s licensing model. Both 2.4GHz and 5GHz are unlicensed. Meaning you don’t need to check with anyone to use those frequencies. (Albeit DFS channels have a process by which APs must move off a channel if an existing incumbent primary user uses the frequencies. But this is totally automatic and NOT a “negotiation”.)

The FCC has designed an innovative licensing scheme that allows for current incumbent users of those frequencies, as well as new users to co-exist and even thrive. Users of these frequencies fall into one of the following distinct groups:

1. Incumbent Users (IU) – These users have the highest priority and all others must not use these channels in any way that could interfere with the incumbent users. This is accomplished by the use of a special spectrum database. This is called the Spectrum Allocation Service or SAS.

For any specific location, one can query SAS and be allowed access to the frequencies if no Incumbent User is already using the frequencies at that specific location.

2. Priority Access Users (PAL) – These are those users of the spectrum that have been willing to pay for priority access to the frequencies. These fees are not yet defined but are to be in the ‘lightly licensed’ category. There are rules limiting the number of channels anyone PAL can access in any given area. These users also have to query SAS to get permission as well as to register their licensed claims.

3. General Authorized Access (GAA) – These users are those who want unlicensed and unpaid access to the CBRS frequencies. They must constantly query the SAS database to determine if they can use frequencies. If no Incumbent User or no Priority Access User is using a specific frequency at a specific location, these frequencies are available for GAA use.

Potential Uses for CBRS

There are a series of potential uses for CBRS frequencies and equipment. But we are going to focus on two specific use cases. The first is Private LTE. Where an enterprise provides a Wireless Infrastructure based on CBRS frequencies and equipment and uses them for in-house communications. These can deliver very high quality and dedicated capacity – something that isn’t always possible with the unlicensed Wi-Fi in 2.4 GHz and 5 GHz since we are required to share those with all other users.

The second option for CBRS is to integrate a system – like the Private LTE above with as an In-Building Cellular Network. Kind of like a replacement for Distributed Antenna Systems (DAS) – in a neutral host scenario where your internal Private LTE connects your users directly to their cell carrier of choice.

Why Wireless LAN Engineers?

Cellular networks, using other types of technologies like CDMA, TDMA, FDMA, GSM, LTE, etc. have long been the domain of a group of cellular engineers. They work in a world mostly without network protocols like TCP/IP and definitively work where the network infrastructure is owned, controlled, and operated by a single entity. That infrastructure also is designed using protocols that rely on centralized control – cell towers tell cell phones what to do, what tower to be on, how loud to transmit, and what slice of spectrum and technique they should use.

By contrast, Wireless LAN Engineers work in a world where the client devices make most of the decisions, where the infrastructure rides on top of a TCP/IP wired network, and where each enterprise owns and operates their own infrastructure. Then the enterprise infrastructure is connected to the wider world via WAN links.

CBRS as currently defined is far closer to the Wi-Fi world than the Cellular world. Even those the transport protocol is LTE – the CBRS infrastructure resembles Wireless LANs. Individual Access Points (CBRS term is eNode B or base station or CBSD – Citizen’s Broadband Service Device) – each connected via Cat5e or Cat6 cable to a wired/switched infrastructure. Transported over a TCP/IP infrastructure and then finally delivered to the wider world over some sort of WAN link.

The design and installation process is very much like the current Wireless LAN design and installation practices.

Conclusion

As a Wireless LAN Engineer, you might want to start preparing and learning about CBRS – you are the ones that might be called on to implement these services.

Learn some of its unique language, new hardware, and how these might integrate with your existing network.

You can thank me later.


As a final note, I hear the following question a lot – and figured it might make a nice postscript to this blog post.

But what about hardware? Is CBRS ready for market?

Currently – Apple’s iPhone 8 sold in Japan has CBRS frequency support – as do some Samsung Galaxy phones in that market. Meaning, the smartphone vendors have already worked out the details to get CBRS radios, antennas, etc. working in their devices

There are also an entire series of Mobile Hotspots and Gateways that take CBRS and convert it to standard 802.11 Wi-Fi and/or 802.3 Ethernet.

Finally – there are many vendors already with CBSD’s (CBRS Access Points) from Corning, Ericsson, Nokia, Ruckus and others.

Not to mention Qualcomm has been developing and shipping Wi-Fi compatible chipsets with CBRS capabilities for a long time now.